Causes and Consequences of Climate Influences on Distribution and Habitat Selection of Migratory Birds

Duration: January 1999 - May 2003

If we are to manage biological diversity successfully in the face of global climate change, we must first understand how climate and vegetation interact to affect the distributions and coexistence of species. As habitat conditions change in response to climate change, the geographic distributions of many plant and animal species may shift. These shifts could yield new combinations of species and create new interactions, such as predation, that could affect population health. Understanding the potential effects of such shifts will enable us to provide managers with guidelines that will help them minimize negative consequences of climate change.

Topographic features in landscapes, such as mountainsides and hill slopes, create localized climatic gradients known as "microclimate gradients." These gradients are small-scale versions of climate conditions that otherwise occur over broad geographic scales. Because segregation of species along microclimate gradients commonly reflects segregation in broader, geographic ranges, studying the responses of species to microclimate gradients can provide insights into climate influences on geographic distributions, habitat selection, and biological interactions that are virtually impossible to examine at the scale of geographic ranges.

This project continues our long-term (10+ years) study of migratory birds along a topographic, microclimate gradient in a high elevation system in central Arizona. We are examining nesting habitat choice in relation to microclimate, microhabitat, parental care and nest predation.

Our long-term data show that four migratory, ground-nesting bird species segregate along a gradient in microclimate (temperature and humidity) and vegetation in their nest site choices.

In this system, Orange-crowned and Virginia's Warblers define two ends of the microclimate spectrum: Orange-crowned Warblers nest in moist sites down low on the slopes and Virginia's Warblers nest in hotter, drier sites, up high.

This local difference is reflected in these species' broader, geographic ranges. The range of Orange-crowned Warblers is largely northern, cool, moist areas, whereas Virginia’s Warblers primarily occur in southern, drier areas.

Building upon our previous work with these four migratory bird species, we will examine differences in sensitivities to changes in climate in terms of spatial distribution, habitat choice, fecundity, demography (population characteristics), physiological constraints and biotic consequences.

Approach

The objectives of the project are to:

1. Assess the relative sensitivity of different species to climate change.

• Do these migratory bird species differ in their sensitivity to climate change and do differences reflect distributional differences?  This question will be answered by measuring differences in nest site location, species abundance and fecundity among years with contrasting weather, and comparing results for different species.
  
  
• Do species with greater spatial and microhabitat shifts in response to climate change experience reduced demographic costs?  Reproductive success and survival will be compared for individuals that move different distances from the median yearly location.

2. Identify causal mechanisms and costs of nest-site shifts.

• Do bird species shift their spatial and microhabitat distributions in order to select similar microclimates from year to year? The microclimates of nests will be measured using portable dataloggers with probes for temperature, humidity, solar radiation and wind speed.
  
  
• What are the energetic costs of shifts in microhabitats?  We will compare the energetic costs exerted on eggs, nestlings and adults by shifts in microhabitat.
  
  
• Why does nest predation increase with shifts in distribution?  Shifts in distribution can cause clear costs in nest predation. We will examine the causes of increased nest predation as a result of shifts in location.

3. Assess the role of scale. 

• How do range limits and dependence up on dry versus moist habitat conditions for nesting interact to determine different species' microhabitat preferences?  We will use a combination of field experiments manipulating nest microclimate conditions, and models from a nation-wide database of breeding birds to address this question. 

Products

This project will yield reports and peer-reviewed publications documenting the distributional and demographic effects of climate change, and the physiological mechanisms underlying these effects.

	More Information Primary Contact: Dr. Tom Martin, USGS Montana Cooperative Wildlife Research Unit E-mail Dr. Martin Related Sites:  Herbivore Exclusion Experiment North American Breeding Bird Survey Project Web Site at University of Montana Tom Martin's Publications (PDF files)